The people who have mentioned just lay low and spy on her to see if she is still doing it are crazy. If your engine in your car was leaking oil and making a funny noise would you just wait to see if it seizes? What good is it to be in a relationship with no sense of trust where you have to spy on your spouse? I would guess that 99% of relationships like that are not lasting long.
Do you want to know the truth or her version of it? Trust me when I say I have been there and the only way to ever know is to not raise her awareness and to let her remain comfortable. I can remember finding things that I thought were wrong and rushing in to confront the issue and never knowing if I had the story or not. The last time I found something that looked fishy I sat on it and watched her. I promise you I got a lot more info that way and also you don't run the risk of making accusations that might not be true.
To each their own. I found a lot more peace with the 2nd method than I ever did trying to get the truth out of a woman.
So how'd that relationship work out? I'm guessing not too well. The bottom line is if you have to spy on your wife and there is no trust then the chances of the relationship ever working are slim and none. The only chance this relationship has to work is for all the cards to be put on the table from the start by both sides. Then it will still take a lot of hard work on both sides to heal, forgive and move on. Spying isn't going to solve anything.
To each their own. I wouldn't call it "spying" in this case. That implies insecurities by the guy that aren't justified and also an on going thing. Some times you find out you jumped to conclusions and every thing is fine. The type of person who cheats will be more than willing to lie. The chances of a person ever putting all the cards on the table are very slim. The chances of a cheater changing are slim. I think you just find out on your own and make a decision based on what you find out and what you can live with. I don't mean to be insulting but I wish things worked out how you say but it has never been my experience.
In this day and age it is rare for a woman who is hot not to be presented with opportunities to cheat. Then you combine all the distractions that simply did not exist in the old days for men; video games, non-stop sports broadcasts, fantasy/easy access to betting, and that provides excellent justification for a woman to stray. Anyone in a relationship nowadays should have their radar up. Talking to her does nothing, and anyways, in this case she obviously is cheating. If some older dude is comfortable enough to be texting a married woman several times a day, including o Christmas Eve, that means there is sex happening.